Sudan has given the country director for the U.S.-based aid agency CARE 72 hours to leave the country, the latest in a series of expulsions of western envoys. As Nick Wadhams reports from Nairobi, it is also seen as part of a systematic clampdown on humanitarian agencies working in the Darfur region.

The Sudanese government delivered the expulsion letter to Paul Barker on Saturday. No reason for the expulsion was given, but Barker says it may have to do with an internal e-mail he wrote a year ago about safety precautions that CARE staff should take in the Darfur region.

CARE's Nairobi-based spokeswoman, Bea Spadacini, says the group had been given no warning about Barker's expulsion, but CARE would not stop working in Sudan. She says CARE employs 550 people in Sudan and the memos like the one Barker wrote are routine.

"According to Paul, this was leaked and the government was irritated by this and it is surprising because we are one of the few organizations that has been able to operate all along," said Spadacini. "It does not mean that all of a sudden CARE has stopped working there. It does not mean like everyone has to evacuate. So I do not know what the implications are, but it is a clear signal of discontent if you are kicking out the country director. It is a signal to the organization."

Sudanese Foreign Ministry spokesman Ali Sadiq Ali refused to comment on the expulsion and Sudan's Humanitarian Aid Commission could not be reached for comment. CARE, which is based in Atlanta, has been working in Sudan for 27 years and estimates it has spent $60 million in Sudan during the past three years.

Spadacini refused to comment on the conditions that CARE works under in Sudan, but numerous aid groups in the past have reported that the Sudanese government monitors them closely, often limits their movement, and in some cases even must approve their news releases.

The expulsion was only the latest ordered by the Sudanese government. The lead Canadian and European Union envoys were ordered out last week, though the E.U. envoy will be allowed to return to finish his term.

And most famously Sudan expelled top U.N. envoy for Sudan Jan Pronk, after he posted a blog entry about the difficult humanitarian situation in Sudan.

The United States has suggested that Sudanese President Omar al-Bashir's government may be using the expulsions to stall international efforts to quell the ongoing crisis in Darfur, where about 200-thousand people have been killed in four years of conflict between local rebels and government-backed militias.

Late last month, the U.N. Security Council overcame Sudan's long-standing objections and approved a 26,000 member peacekeeping force for Darfur. But some of the rebel groups say they are reconsidering whether to join future peace talks because of ongoing raids by government forces and the militias.